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Caution Underspeed

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jimmyz80 View Drop Down
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    Posted: 28 Jan 2017 at 6:38pm
Ever since i had my DFC90 installed, I've been getting super annoying "Caution, Underspeed" warnings on landing rollout.  So you're rolling down the runway listening for exit instructions from the tower, and the DFC is bitching and complaining that I'm going too slow. :)

I assume this doesn't happen to everyone, or it would be a much bigger deal.  Any ideas as to why this would be happening?
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Melohn View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Melohn Quote  Post ReplyReply Direct Link To This Post Posted: 29 Jan 2017 at 2:14am
Assuming you have a Cirrus, you are hearing this because your flap switch is not connected to the DFC90, so it assumes that you are flying with flaps up.

You have two choices; have the flap switch connected to the DFC90, or always use the autopilot disconnect when operating at speeds below ~80 knots; you won't hear the caution when the autopilot is in AP READY state.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote jimmyz80 Quote  Post ReplyReply Direct Link To This Post Posted: 29 Jan 2017 at 1:30pm
The flap switch is properly connected, since I get the appropriate flap overspeed warnings.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jimmyz80 Quote  Post ReplyReply Direct Link To This Post Posted: 25 Sep 2018 at 8:30pm
Bumping this back to the top since I had forgotten about it, but the warnings still continue.  The flap switch is definitely connected to the DFC90 since I get flap overspeed warnings as appropriate.  But when landing, even with the AP and FD fully disengaged, I still get underspeed warnings on roll-out.  It's super duper annoying since it's inevitably talking over the top of a tower controller trying to give me runway exit instructions.

Any ideas why it would be doing this?
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Ibraham View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ibraham Quote  Post ReplyReply Direct Link To This Post Posted: 27 Sep 2018 at 2:33pm
Do you retract the flaps on rollout? try to keep the flaps extended until you exit the runway to see if you still get the alert. 

On some configurations, full flaps condition suppresses the "underspeed" alert. You could look at the DFC90 Pilot Guide Section 6 "Limitations and Performance" table for your specific configuration.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jimmyz80 Quote  Post ReplyReply Direct Link To This Post Posted: 27 Sep 2018 at 2:43pm
I tried that test as well on recent flights, and I get the warning regardless of whether I leave in 100% flaps or retract them while rolling.  I see some notes about the warnings being suppressed when "near idle" but that's not quantified in any way.  Many times I still have a little taxi power re-applied on the ground to clear the runway quickly at large airports.  I have no way to know if that still qualifies as "near idle".
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ibraham Quote  Post ReplyReply Direct Link To This Post Posted: 27 Sep 2018 at 3:24pm
See this SIL from Avidyne (page 6), it addresses Underspeed Alerting in DFC90 and SIU-Equipped Cirrus Aircraft

https://www.avidyne.com/files/downloads/606-00006-002.pdf

SR22 S/N:1663 and on have DAU (Cirrus SR22 S/N 435-1662 have SIU)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Melohn Quote  Post ReplyReply Direct Link To This Post Posted: 27 Sep 2018 at 9:23pm
I read the SIL, but it didn’t seem clear to me what happens in an SIU aircraft with R2 software and latest PFD software that does NOT have the flap modification. It would seem as though the logic should say, no flap input, no Manifold Pressure input, no alerting, but it wasn’t clear to me that’s the case. I happen to have that configuration, but am still running R1, which does not provide the warnings unless you leave the AP in FD mode. I’m quite happy with this, but fear someday I’ll need to send in my DFC90 and it will come back with new software.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote jimmyz80 Quote  Post ReplyReply Direct Link To This Post Posted: 08 Oct 2018 at 1:05pm
Originally posted by Ibraham Ibraham wrote:

See this SIL from Avidyne (page 6), it addresses Underspeed Alerting in DFC90 and SIU-Equipped Cirrus Aircraft

https://www.avidyne.com/files/downloads/606-00006-002.pdf

SR22 S/N:1663 and on have DAU (Cirrus SR22 S/N 435-1662 have SIU)

My aircraft is DAU equipped, so this SIL doesn't apply.
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